A continuum theory for confined hard-sphere polymers is presented. Starting from fundamental relations and applying defined approximations, a constitutive relation for the conformation probability (analogous to the result in mean-field lattice theories) is developed. The main problem of hard-sphere correlations is attacked by two approximate methods: First, using the Carnahan-Starling equation of state and local volume fractions (CS). Second, by an extension of the lattice theory to spherical components with unequal volumes (LATT). The agreement with Monte Carlo simulations is good for both approximations at low densities, but becomes only qualitative at the higher concentrations. The CS approximation seems to be favored over the LATT approach at the higher concentrations when correlation becomes more important. Both free and grafted chains are treated. The influence of chain length, grafting density, solvent concentration, solvent chain length, and surface curvature on the segment distribution is investigated.

2.

Björling, Mikael

et al.

Royal Institute of Technology, Physical Chemistry, Stockholm, Sweden.

Pellicane, G.

Dipartimento di Fisica, Sez. Teorica, Messina, Italy; Ist. Nazionale Fisica della Materia, Messina, Italy.

Caccamo, C.

Dipartimento di Fisica, Sez. Teorica, Messina, Italy; Ist. Nazionale Fisica della Materia, Messina, Italy.

Flory-Huggins (FH) and integral equation theories (IETs) are used to describe the equation of state and the relevant mixing properties of hard sphere binary mixtures in the limit of high size-asymmetry. The results are compared with those obtained from the heuristic equation of state of Mansoori et al. (BMCSL) [J. Chem. Phys. 54, 1523 (1971)] and with the Flory-Huggins scheme of other authors. By choosing a physical recipe for the volume fractions of the two species in the mixture FH theory is shown to be a good approximation to the entropy and the Gibbs free energy of mixing, which shows improvement at high size-asymmetry. In addition, the results of the IETs are found to be in overall quantitative agreement with BMCSL. The implications of our study concerning colloidal systems are discussed.

3.

Halle, B.

et al.

Condensed Matter Magnetic Resonance Group, Lund University, Chemical Center, Lund, Sweden.

Björling, Mikael

Laboratoire S.R.S.I., U.R.A. C.N.R.S. 1662, Université P. et M. Curie, Paris, France; Division of Physical Chemistry, Royal Institute of Technology, Stockholm, Sweden.

Microemulsions as macroelectrolytes1995In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 103, no 4, p. 1655-1668Article in journal (Refereed)

Abstract [en]

Water-in-oil microemulsions, composed of discrete aqueous droplets dispersed in a continuous oil medium, constitute a special class of electrolyte solutions. Such macroelectrolytes are analogous to conventional electrolyte solutions in most respects, with the notable difference that, in a microemulsion, the ionic (droplet) charge is not fixed but depends on the droplet interactions. Describing the microemulsion as a primitive-model electrolyte mixture with ions of variable charge and evaluating the statistical mechanics within the mean-spherical approximation (MSA), we construct a self-consistent theory of charge fluctuations and droplet interactions in ionic microemulsions. The droplet charge distribution is calculated as a function of the size, shape, polydispersity, and volume fraction of the droplets. We argue that the net droplet charges can have a decisive influence on microemulsion structure, especially at the higher volume fractions where clustering and spinodal decomposition are observed. At lower volume fractions, where the MSA treatment should be quantitatively accurate, the Coulomb interaction between charged droplets has no effect on the structure factor deduced from scattering data.

4.

Mirsakiyeva, Amina

et al.

Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden.

Hugosson, Håkan W.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Physics.

Linares, Mathieu

Department Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, Stockholm, Sweden; 4Swedish e-Science Research Center (SeRC), KTH Royal Institute of Technology, Stockholm, Sweden.

Delin, Anna

Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden; Swedish e-Science Research Center (SeRC), KTH Royal Institute of Technology, Stockholm, Sweden; Department of Physics and Astronomy, Materials Theory Division, Uppsala University, Uppsala, Sweden.

The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexible electronics. We present combined molecular dynamics and quantum chemical calculations, based on density functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS and EDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems. With finite size scaling, we also extrapolate our results to the infinite polymers, i.e., PEDOT, PEDOS, and PEDOTe. Our computations indicate that the most favourable oligomer conformations at finite temperature are conformations around the flat trans-conformation and a non-flat conformation around 45° from the cis-conformation. Also, the dihedral stiffness increases with the atomic number of the heteroatom. We find excellent agreement with experimentally measured gaps for PEDOT and PEDOS. For PEDOT, the gap does not increase with temperature, whereas this is the case for its derivatives. The conformational disorder and the choice of the basis set both significantly affect the calculated gaps.

Based on the Euler-Lagrange equation for ion density distribution in an inhomogeneous, charged, and hard-sphere fluid, a novel method is proposed to determine the interaction pressure between charged plates. The resulting expression is a sum of distinct physical contributions to the pressure, which involves different contributions to the single-particle direct correlation function. It can, therefore, be conveniently used in any density functional approach to facilitate analysis of the pressure components. In this study, the so-called fundamental measure theory (FMT)/weighted correlation approach (WCA) approach is applied to estimate both the hard-sphere and the electric residual contributions to the single-particle direct correlation function, upon the calculation of the ionic density profiles between charged plates. The results, against the Monte Carlo simulations, show that the FMT/WCA approach is superior to the typical FMT/mean spherical approximation approach of the density functional theory in predicting the interaction pressure between charged plates immersed in an electrolyte solution upon various conditions in the primitive model. The FMT/WCA approach can well capture the fine features of the pressure-separation dependence, to reproduce not only the shoulder shape and the weak attractions in monovalent electrolytes but also the strongly oscillatory behavior of pressure in divalent electrolytes where pronounced attractions are observed. In addition, it is found that the FMT/WCA approach even has an advantage over the anisotropic, hyper-netted chain approach in that it agrees with the Monte Carlo results to a very good extent with, however, much less computational effort.